Mustang T56 Shifting Problems

I have a 01 mustang with a tremec 6 speed manual in it. I was at the track yesterday when my clutch decided to stop working half way down the track. It was like there was pressure on the pedal and I couldn't push it down. i turned the car off and turned it back on worked fine drove it half a mile did the same thing, every time I can just turn it off and back on and it fixes it completely. Any ideas? Also I put a new cable quadrant and adjuster in.